EP0486333A1 - Process for the preparation of 1,1,1,2-tetra fluoroethane - Google Patents

Abstract

The invention relates to the manufacture of tetrafluoro-1,1,1,2 ethane (F134a) by catalytic fluorination of chloro-1-trifluoro-2,2,2-ethane (F133a) in the gas phase. A mixed catalyst is used which is composed of oxides, halides and / or oxyhalides of nickel and chromium deposited on a support consisting of aluminum fluoride or a mixture of aluminum fluoride and alumina. This mixed catalyst provides excellent selectivity for F134a with high productivity.

Description

The present invention relates to the manufacture of tetrafluoro-1,1,1,2 ethane by catalytic fluorination of chloro-1-trifluoro-2,2,2-ethane in the gas phase using hydrofluoric acid.

Tetrafluoro-1,1,1,2 ethane (known in the trade under the designation F134a) is a potentially interesting compound to replace dichlorodifluoromethane (F12) currently used as refrigerant, but suspected of contributing to the weakening of the layer stratospheric ozone. Economic methods are therefore currently being sought for industrially producing F134a, one of these being the fluorination of chloro-1-trifluoro-2,2,2-ethane (known in the art under the designation F133a).

The catalytic fluorination of chlorinated or brominated hydrocarbons in the gas phase using hydrofluoric acid is a known method of access to fluorinated hydrocarbons.

Thus, in US Pat. No. 2,744,147, an alumina-based catalyst promoted by a metal (cobalt, nickel or chromium) has been described and its use in a fluidized bed for the fluorination of haloalkanes at a temperature between 180 and 425 ° C. This patent relates more specifically to the fluorination of haloalkanes containing 1 or 2 carbon atoms, at least one of which carries at least two halogen atoms having an atomic number equal to or less than 35, at least one of these halogen atoms being chlorine or bromine.

The same is true in US Pat. No. 2,744,148 which describes an alumina catalyst promoted by a metal (chromium, cobalt, nickel, copper or palladium) and its use for the fluorination of haloalkanes into highly fluorinated products. This patent also describes a process for activating the catalyst and converting part of the alumina to basic aluminum fluorides.

No indication is provided in these US patents with regard to the duration of operation over time of these catalytic formulas. Furthermore, no example describes the fluorination of chloro-1-trifluoro-2,2,2-ethane, a fluorination which has the particularity of being a balanced reaction leading to partial conversions of the raw material and in which, for elsewhere, the formation of unsaturated compounds gives rise to fouling phenomena of the catalysts by deposition of coke, which affects their lifetime.

US Pat. No. 3,514,253 describes catalysts based on aluminum fluoride impregnated with copper, cobalt, chromium or nickel salts and their use in the fluorination of aromatic (trichlorobenzene) or cyclic (octachlorocyclopentene) compounds.

The fluorination process described in US Pat. No. 4,147,733 for the manufacture of trifluoro-1,1,1 ethane or difluoromethane in the presence of aluminum fluorides, chromium and / or nickel, is characterized in that one adds water vapor to the reagents. This process does not apply to tetrafluoro-1,1,1,2 ethane whose chlorinated precursor (1-chloro-trifluoro-2,2,2 ethane) can react with water under the operating conditions described.

Patent FR 2 014 711 claims a process for the fluorination of haloalkanes, especially that of 1,1,2-trichloro-1,2,2 trifluoro-ethane to 1,2-dichloro-1,1,2,2-tetrafluoroethane using a catalyst consisting of aluminum fluoride and small amounts of iron, chromium and possibly nickel compounds; this catalyst is also suitable for chlorofluorination of ethylene. In the first reaction, the NiF ₂ / AIF ₃ catalyst turns out to be more active than the mixed catalyst: (NiF ₂ + CrF ₃ ) / AIF ₃ (see tests 2 and 6 in Table 1 on page 9). For the same type of fluorination, US Pat. No. 3,793,229 describes the use of zinc, chromium and nickel catalysts supported on AIF ₃ , and US Pat. No. 3,787,331 that of manganese, chromium and optionally nickel catalysts supported on AIF ₃ . None of these three patents mentions the fluorination reaction of chloro-1-trifluoro-2,2,2 ethane.

Patent application WO 89/10341 claims a process for fluorinating saturated or unsaturated compounds in the presence of a catalyst based on very pure alumina (containing less than 100 ppm of sodium, and porous) serving as a support for metal fluorides (nickel, cobalt, iron, manganese, chromium, copper or silver). This technique, which requires a high purity catalyst, leads in particular to selectivities for tetrafluoro-1,1,1,2 ethane which are high but often less than 97.5% and a productivity often less than 65 g / hour per liter. of catalyst.

In patent SU 466,202 a method of fluorination of vinyl chloride is described in the presence of a catalyst consisting of aluminum fluoride, nickel fluoride and chromium oxide. No mention is indicated on the preparation of the catalyst, its lifetime, nor especially on its activity in the synthesis of tetrafluoro-1,1,1,2 ethane.

Patent applications EP 0 328 127 and 0 331 991 relate specifically to the manufacture of tetrafluoro-1,1,1,2 ethane by catalytic fluorination of chloro-1-trifluoro-2,2,2 ethane in the gas phase using hydrofluoric acid. According to document EP 0 328 127, the operation is carried out in the presence of oxygen and uses a catalyst comprising a metal chosen from the group consisting of Co, Mn, Ni, Pd, Ag and Ru on an aluminum fluoride support. In the process of document EP 0 331 991, a catalyst is used comprising a metal from groups VIII, VIIB, IIIB, IB or a metal having an atomic number from 58 to 71, on a support of aluminum fluoride or carbon. Example 5 of this last document shows that with a nickel catalyst, at 350 ° C. with a contact time of 30 seconds and an HF / F133a molar ratio of 10, the conversion rate of the F133a is only 8% and the selectivity for F134a is only 86.3%; an increase in temperature (400 and 425 ° C. in Examples 6 and 7) improves the conversion rate of F133a, but does not appreciably modify the selectivity to F134a which remains at around 85%.

It has now been found that a very high F134a selectivity (close to 100%) can be obtained by using a mixed catalyst based on nickel and chromium.

The subject of the invention is therefore a process for the manufacture of tetrafluoro-1,1,1,2 ethane (F134a) by catalytic fluorination of chloro-1-trifluoro-2,2,2 ethane (F133a) in the gas phase using hydrofluoric acid, characterized in that a mixed catalyst is used composed of oxides, halides and / or oxyhalides of nickel and chromium deposited on a support consisting of aluminum fluoride or a mixture of fluoride aluminum and alumina.

This catalyst can be prepared in a manner known per se from an activated alumina. This can in a first step be transformed into aluminum fluoride or a mixture of aluminum fluoride and alumina, by fluorination using air and hydrofluoric acid, the transformation rate of the alumina in aluminum fluoride depending essentially on the temperature at which the fluorination of the alumina is carried out (generally between 200 and 450 ° C, preferably between 250 and 400 ° C). The support is then impregnated using aqueous solutions of chromium and nickel salts or using aqueous solutions of chromic acid, nickel salt and methanol (serving as a reducing agent for chromium).

Chlorides are preferred as the chromium and nickel salts, but other salts such as, for example, oxalates, formates, acetates, nitrates and sulfates or nickel dichromate can be used, provided these salts are soluble. in the amount of water likely to be absorbed by the support.

The catalyst used in the process according to the invention can also be prepared by direct impregnation of the activated alumina using the solutions of the chromium and nickel compounds mentioned above. In this case, the transformation of at least part (70% or more) of the alumina into aluminum fluoride is carried out during the activation step of the catalyst.

The activated aluminas to be used for the preparation of the catalyst according to the present invention are well known products, available commercially. They are generally prepared by calcining alumina hydrates at a temperature between 300 and 800 ° C. Activated aluminas, which can be used in the context of the present invention, may contain significant contents (up to 1000 ppm) of sodium without this adversely affecting the catalytic performance.

The catalyst according to the invention may contain by weight from 0.5 to 20% of chromium and from 0.5 to 20% of nickel and, preferably, between 2 and 10% of each of the metals in an atomic nickel / chromium ratio. between 0.5 and 5, preferably close to 1.

Before being able to catalyze the fluorination reaction from F133a to F134a, the catalyst according to the invention must be conditioned, that is to say transformed into active and stable constituents (under reaction conditions) by a prior operation called activation.

• - séchage à basse température (100 à 150°C, de préférence 110 à 120°C) en présence d'air ou d'azote,
• - séchage à haute température (350 à 450°C, de préférence 390 à 410°C) sous azote,
• - fluoration à basse température (180 à 300°C, de préférence à 200°C environ) au moyen d'un mélange d'acide fluorhydrique et d'azote, en contrôlant la teneur en HF de façon que la température ne dépasse pas 300°C, et
• - finition sous courant d'acide fluorhydrique pur à une température pouvant aller jusqu'à 450°C.

This treatment can be carried out either "in situ" (in the fluorination reactor) or else in suitable equipment designed to withstand the activation conditions. This generally includes the following steps:

• - drying at low temperature (100 to 150 ° C, preferably 110 to 120 ° C) in the presence of air or nitrogen,
• - drying at high temperature (350 to 450 ° C, preferably 390 to 410 ° C) under nitrogen,
• - fluorination at low temperature (180 to 300 ° C, preferably at around 200 ° C) using a mixture of hydrofluoric acid and nitrogen, controlling the HF content so that the temperature does not exceed 300 ° C, and
• - finishing under pure hydrofluoric acid current at a temperature of up to 450 ° C

During this operation, the catalytic precursors (nickel and chromium halides, nickel chromate or dichromate, chromium oxide) are transformed into the corresponding fluorides and / or oxyfluorides, which gives off water and / or hydrochloric acid. .

The chemical analysis of the elements (chromium, nickel, fluorine, aluminum, oxygen), after this activation, makes it possible to verify the mineral composition of the catalyst according to the invention.

• a) Le catalyseur peut fonctionner soit en lit fluidisé, soit en lit fixe. On préfère le second mode de fonctionnement car la réaction s'avère pratiquement athermique.
• b) La température de réaction dépend de la pression de fonctionnement. A pression atmosphérique la température de réaction est comprise entre 300 et 375°C et, de préférence, comprise entre 330 et 360°C ; à plus haute pression (vers 15 bars absolus), la température optimale est comprise entre 350 et 420°C et, de préférence, comprise entre 375 et 410°C.
• c) Le rapport molaire HF/F 133a peut varier entre 1 et 20, mais de préférence entre 2 et 5.
• d) Le temps de contact, calculé comme le temps de passage des gaz (dans les conditions réactionnelles) à travers le volume de catalyseur en vrac, est compris entre 2 et 30 secondes. Il est de préférence compris entre 3 et 5 secondes sous pression atmosphérique et entre 5 à 25 secondes sous plus forte pression (vers 15 bars absolus).
• e) L'addition d'oxygène pour maintenir l'activité catalytique n'est pas obligatoire et dépend des conditions de fonctionnement du catalyseur. Dans des conditions qui fournissent la productivité la plus élevée, et lorsque l'on désire une durée de vie compatible avec une application industrielle, la régénération continue ou discontinue du catalyseur peut être réalisée en présence d'oxygène ; sa concentration dans les gaz (réactifs ou inerte) doit alors être suffisante pour entraîner la combustion des produits carbonés responsables de la désactivation.
• f) La pression de fonctionnement est comprise entre 1 et 20 bars absolus, de préférence comprise entre 12 et 16 bars absolus.

The operating conditions for the synthesis of tetrafluoro-1,1,1,2 ethane (F134a) by fluorination of chloro-1-trifluoro-2,2,2 ethane (F133a) in the gas phase using hydrofluoric acid in the presence of the catalyst according to the invention are the following:

• a) The catalyst can operate either in a fluidized bed or in a fixed bed. The second mode of operation is preferred since the reaction turns out to be practically athermal.
• b) The reaction temperature depends on the operating pressure. At atmospheric pressure, the reaction temperature is between 300 and 375 ° C and preferably between 330 and 360 ° C; at higher pressure (around 15 bar absolute), the optimum temperature is between 350 and 420 ° C and preferably between 375 and 410 ° C.
• c) The HF / F 133a molar ratio can vary between 1 and 20, but preferably between 2 and 5.
• d) The contact time, calculated as the passage time of the gases (under the reaction conditions) through the volume of bulk catalyst, is between 2 and 30 seconds. It is preferably between 3 and 5 seconds at atmospheric pressure and between 5 to 25 seconds at higher pressure (around 15 bar absolute).
• e) The addition of oxygen to maintain the catalytic activity is not compulsory and depends on the operating conditions of the catalyst. Under conditions which provide the highest productivity, and when a service life compatible with an industrial application is desired, continuous or discontinuous regeneration of the catalyst can be carried out in the presence of oxygen; its concentration in the gases (reactive or inert) must then be sufficient to cause the combustion of the carbonaceous products responsible for deactivation.
• f) The operating pressure is between 1 and 20 bar absolute, preferably between 12 and 16 bar absolute.

The following examples illustrate the invention without limiting it.

EXAMPLE 1 1A - PREPARATION AND ACTIVATION OF THE CATALYST

• - forme : billes de 1-2 mm de diamètre
• - surface BET : 223 m²/g
• - volume poreux : 1,2 cm³/g (pour les rayons de pores compris entre 40 A et 63 microns)
• - teneur en sodium : 900 ppm

In a rotary evaporator, 250 ml of a support are placed containing by weight 73% aluminum fluoride and 27% alumina, obtained in a previous step by fluorination of GRACE HSA alumina in a fluidized bed at around 300 ° C. using air and hydrofluoric acid (volume concentration of 5 to 10% of this acid in the air). The GRACE HSA starting alumina has the following physicochemical characteristics:

• - shape: beads of 1-2 mm in diameter
• - BET surface: 223 m ² / g
• - pore volume: 1.2 cm ³ / g (for pore radii between 40 A and 63 microns)
• - sodium content: 900 ppm

• a) solution chromique additionnée de chlorure de nickel contenant :
  

• b) solution méthanolique contenant :
  

Two separate aqueous solutions are also prepared:

• a) chromic solution containing nickel chloride containing:
  

• b) methanolic solution containing:
  

The mixture of these two solutions is then introduced, at ambient temperature under atmospheric pressure and in approximately 45 minutes, onto the support with stirring. The catalyst is then dried under a stream of nitrogen, in a fluidized bed, at 110 ° C. for 4 hours.

100 ml (72 g) of dry catalyst are loaded into an INCONEL tubular reactor with an internal diameter of 27 mm and the temperature is raised to 120 ° C. under a stream of nitrogen, at atmospheric pressure. This treatment is maintained for 15 hours then the nitrogen is replaced by air at the same temperature for 4 hours. The temperature is then brought to 400 ° C. under a stream of nitrogen, then maintained for 14 hours (heating time included).

The temperature is then brought back to 200 ° C. under a stream of nitrogen for 15 hours and the nitrogen is then gradually replaced by hydrofluoric acid, taking care that the temperature increase does not exceed 95 ° C. .

Finally, the temperature is raised to 450 ° C. under a stream of pure hydrofluoric acid (1 mol / hour) for 6 hours.

• - composition chimique (pondérale)
  
  
• - propriétés physiques :
  

It is finally lowered to 350 ° C (under a stream of nitrogen) to start the catalytic test. The physicochemical properties of the catalyst thus dried and activated are as follows:

• - chemical composition (by weight)
  
  
• - physical properties :
  

1B - FLUORINATION OF F133a IN F134a

• - volume de catalyseur (en vrac) : 75 ml
• - température : 350°C
• - pression : atmosphérique
• - débit d'acide fluorhydrique : 1,09 moles/h
• - débit de F133a : 0,26 moles/h c'est-à-dire un rapport molaire HF/F 133a = 4,2 ± 0,3 et un temps de contact de 3,9 ± 0,2 secondes dans les conditions réactionnelles.

The performance of the catalyst was tested under the following operating conditions, without the addition of oxygen:

• - volume of catalyst (in bulk): 75 ml
• - temperature: 350 ° C
• - atmospheric pressure
• - hydrofluoric acid flow rate: 1.09 moles / h
• - flow rate of F133a: 0.26 moles / h, that is to say a HF / F 133a molar ratio = 4.2 ± 0.3 and a contact time of 3.9 ± 0.2 seconds under the conditions reactionary.

The gases from the reaction are freed from the hydracids by washing with water, then dried and analyzed by C.P.V.

Table 1 below collates the main results obtained during a 402 hour test of continuous operation on this same catalyst charge.

EXAMPLE 2 2A - PREPARATION AND ACTIVATION OF THE CATALYST

The procedure is as in Example 1A, but replacing the chromic anhydride with chromium trichloride hexahydrate and removing the methanol.

et l'on imprègne 250 ml du même support avec cette solution, en une heure.A single aqueous solution is prepared containing:

and 250 ml of the same support are impregnated with this solution, in one hour.

The rest of the drying and activation treatment is identical to that described in Example 1A.

The chemical composition by weight of the activated catalyst is as follows:

Its physical properties are as follows:

2B - FLUORINATION OF F133a IN F134a

This catalyst was tested under the same operating conditions as those described in Example 1B. The results obtained during a test of 123 hours in continuous operation, without addition of oxygen, are collated in table 2 below.

EXAMPLE 3 (comparative) - CHROME CATALYST WITHOUT NICKEL

The catalyst was prepared and activated by operating exactly as described in Example 1A, but removing the 29 g of nickel chloride hexahydrate in the aqueous solution a).

The chemical composition of the activated catalyst is as follows:

Its physical properties are as follows:

This catalyst was tested under the same operating conditions as those described in Example 1 B. The results obtained during a test of 126 hours in continuous operation, without addition of oxygen, are collated in Table 3 below. after.

The comparison of these results with those of Tables 1 and 2 makes it possible to conclude that the nickelchrome association according to the invention is more active and above all more stable over time.

EXAMPLE 4 4A - PREPARATION AND ACTIVATION OF THE CATALYST

• a) solution chromique de chlorure de nickel contenant :
  
• b) solution méthanolique contenant :
  

The procedure is as in Example 1A (same support) by modifying the proportions of the two aqueous solutions as follows.

• a) chromic solution of nickel chloride containing:
  
• b) methanolic solution containing:
  

The drying and the activation of the catalyst are then strictly carried out as indicated in Example 1A.

• - composition chimique (Pondérale)
  
• - propriétés physiques
  

The physico-chemical properties of the catalyst thus obtained are as follows:

• - chemical composition (Weight)
  
• - physical properties
  

4B - FLUORINATION OF F133a IN F134a

The performance of the catalyst was tested under the following operating conditions:

An HF / F133a molar ratio of between 2 and 2.4, and a contact time of between 16.5 and 17.9 seconds, were maintained during this test.

The gases resulting from the reaction are expanded at atmospheric pressure, freed from the hydracids by washing with water, then dried and analyzed by CPV.

Table 4 below collates the main results obtained during a 54-hour test of continuous operation on this same catalyst charge.

Claims (8)

1. Process for the manufacture of tetrafluoro-1,1,1,2 ethane (F134a) by catalytic fluorination of chloro-1-trifluoro-2,2,2 ethane (F133a) using gaseous hydrofluoric acid, characterized in what is used a mixed catalyst composed of oxides, halides and / or oxyhalides of nickel and chromium deposited on a support consisting of aluminum fluoride or a mixture of aluminum fluoride and alumina. 2. Method according to claim 1, characterized in that the content by weight of the nickel and chromium catalyst is between 0.5 and 20% for each metal, the nickel / chromium atomic ratio being between 0.5 and 5, preferably close to 1. 3. Method according to claim 2, characterized in that the content is between 2 and 10% for each metal. 4. Method according to one of claims 1 to 3, characterized in that the support can contain up to 1000 ppm of sodium. 5. Method according to one of claims 1 to 4, characterized in that the reaction temperature is between 300 and 420 ° C, preferably between 330 and 410 ° C. 6. Method according to one of claims 1 to 5, characterized in that the operating pressure is between 1 and 20 bars, preferably between 12 and 16 bars absolute. 7. Method according to one of claims 1 to 6, characterized in that the HF / F 133a molar ratio is between 1 and 20, preferably between 2 and 5. 8. Method according to one of claims 1 to 7, characterized in that the contact time, calculated under the reaction conditions, is between 2 and 30 seconds, preferably between 5 and 25 seconds.